Post by SKYSUMMIT on Aug 8, 2017 19:24:48 GMT -6
MESOSCALE PRECIPITATION DISCUSSION 0658
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
904 PM EDT TUE AUG 08 2017
AREAS AFFECTED...SOUTHEAST TX...WEST-CENTRAL/SOUTHWEST LA
CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY
VALID 090100Z - 090700Z
SUMMARY...VERY HEAVY RAINFALL FROM SLOW-MOVING SHOWERS AND
THUNDERSTORMS IS EXPECTED THIS EVENING AND ESPECIALLY DURING THE
OVERNIGHT HOURS ACROSS PORTIONS OF SOUTHEAST TX AND POSSIBLY FAR
SOUTHWEST LA. FLASH FLOODING IS LIKELY.
DISCUSSION...A WELL-DEFINED MCV AND AN ASSOCIATED AREA OF SURFACE
LOW PRESSURE CONTINUES TO REMAIN NEARLY STATIONARY OVER SOUTHEAST
TX AND CLOSE TO THE HOUSTON METROPOLITAN AREA. OVER THE LAST FEW
HOURS...THERE HAD BEEN A CURVED BAND OF CONVECTION WITH VERY HEAVY
RAINFALL RATES AROUND THE EASTERN FLANK OF THE LOW
CENTER...GENERALLY IN BETWEEN GALVESTON BAY AND THE
BEAUMONT/PORT-ARTHUR AREA...ALTHOUGH THERE HAS BEEN SOME SUBTLE
WEAKENING OF THIS OVER THE LAST HOUR. REGARDLESS...THE CONVECTION
HAS BEEN SITUATED WITHIN AN AXIS OF LOCALLY ENHANCED SURFACE
MOISTURE CONVERGENCE ALONG WITH PROXIMITY TO A STRONGER
INSTABILITY GRADIENT.
OVER THE NEXT SEVERAL HOURS...THERE IS SUPPORT FROM MULTIPLE HIRES
MODEL SOLUTIONS FOR CONVECTION TO LOCALLY PERSIST AND/OR REDEVELOP
AROUND THE EASTERN FLANK OF THE CIRCULATION GIVEN CLOSE PROXIMITY
TO STRONGER INSTABILITY AND SURFACE/FRICTIONAL CONVERGENCE ALONG
THE UPPER TX COAST. THIS WOULD IMPACT AREAS JUST INLAND OVER
SOUTHEAST TX AND ALSO INTO PARTS OF SOUTHWEST LA. HOWEVER...A
NOCTURNAL TIGHTENING OF THE LOW TO MID LEVEL VORTICITY OVERNIGHT
INVOLVING THE MCV WILL ALLOW CONVECTION TO ATTEMPT TO REFOCUS
CLOSER IN TO THE ACTUAL LOW CENTER NEAR THE HOUSTON/GALVESTON
METROPOLITAN AREAS. THERE WILL BE CONCERNS FOR THIS HAPPENING
TOWARD THE 06Z TIME FRAME.
PWATS ARE BETWEEN 2.25 AND 2.5 INCHES...WITH MOISTURE HIGHLY
CONCENTRATED THROUGH THE VERTICAL COLUMN...AND SUPPORTIVE OF
HIGHLY EFFICIENT RAINFALL PROCESSES. GIVEN THIS AND THE LEVEL OF
INSTABILITY POOLED ALONG THE WESTERN GULF COAST...THE RAINFALL
AMOUNTS MAY EXCEED 3 INCHES/HR WITHIN THESE CONVECTIVE BANDS.
THE POTENTIAL EXISTS ON A SMALL SCALE FOR AS MUCH AS 3 TO 6+
INCHES OF NEW RAINFALL THROUGH THIS VALID PERIOD...WITH THE
GREATEST POTENTIAL GENERALLY IN BETWEEN THE HOUSTON METROPOLITAN
AREA AND BEAUMONT/PORT-ARTHUR. FLASH FLOODING IS LIKELY GIVEN THE
RECENT HEAVY RAINFALL OVER THE LAST 24 HOURS...AND IT COULD BE
QUITE SIGNIFICANT ON A SMALL SCALE INVOLVING ANY OF THE URBANIZED
CORRIDOR AROUND THE HOUSTON/GALVESTON METROPOLITAN AREA AND
INCLUDING THE ADJACENT SUBURBS.
ORRISON
